Introduced a delay after a completed sync before starting msg1 generation:

- this was necessary because as soon as the gNB starts, it tries detecting
  the prach preambles and it mesaures the background noise. However, there is
  a delay of several dozens of frames before it considers the preables as
  detected.
- the solution at the UE consists in avoiding sending preamble as soon as the
  UE syncs by introducing an offset, this keeps the power measurements low at
  gNB side as long as the preamble detection counter is under threshold

openair2/LAYER2/NR_MAC_UE/nr_ra_procedures.c

@@ -353,7 +353,7 @@ void nr_ue_get_rach(NR_PRACH_RESOURCES_t *prach_resources,
 
   AssertFatal(CC_id == 0,"Transmission on secondary CCs is not supported yet\n");
 
-  if (UE_mode == PRACH) {
+  if (UE_mode == PRACH && prach_resources->init_msg1) {
 
     LOG_D(MAC, "nr_ue_get_rach, RA_active value: %d", mac->RA_active);